Usage: head [OPTION]... [FILE]...
默认输出前10行
当指定多个文件时，在输出前输出各个文件名
当没有指定文件或指定的文件是“-”说明读取标准输入

Mandatory arguments to long options are mandatory for short options too.
  -c, --bytes=[-]K         print the first K bytes of each file;
                             with the leading `-‘, print all but the last
                             K bytes of each file 显示头部前多少字节，这里的K是单位的标示，具体的单位参考下面列表，当使用-K时显示除了尾部多少字节外的所有内容
  -n, --lines=[-]K         print the first K lines instead of the first 10;
                             with the leading `-‘, print all but the last
                             K lines of each file显示头部的多少行，默认显示头部10行，例如-n -b代表显示除了尾部512行外的所有行
  -q, --quiet, --silent    never print headers giving file names当指定多个文件时，出现内容中不输出文件名
  -v, --verbose            always print headers giving file names
      --help     display this help and exit
      --version  output version information and exit

K may have a multiplier suffix:
b 512, kB 1000, K 1024, MB 1000*1000, M 1024*1024,
GB 1000*1000*1000, G 1024*1024*1024, and so on for T, P, E, Z, Y.

Usage: tail [OPTION]... [FILE]...
默认输出尾部10行
当指定多个文件时，默认在输出内容前显示文件名
当没有指定文件或者指定的文件是“-”时，读取标准输入

Mandatory arguments to long options are mandatory for short options too.对于长选项不可忽略的参数对应短选项也不可忽略
  -c, --bytes=K            output the last K bytes; alternatively, use -c +K显示尾部的字节数，当使用+k参数时表示从k字节开始显示到末尾，例如-c +1b 显示512字节开始到末尾的内容
                           to output bytes starting with the Kth of each file
  -f, --follow[={name|descriptor}]
                           output appended data as the file grows;
                           -f, --follow, and --follow=descriptor are
                           equivalent追加显示文件最新的内容
  -F                       same as --follow=name --retry等同于使用 -f filename --retry操作
  -n, --lines=K            output the last K lines, instead of the last 10;默认显示输出尾部的10行，当使用+k参数时指从第K行开始显示到末尾，例如-n +6显示第6行到末尾的内容
                           or use -n +K to output lines starting with the Kth
      --max-unchanged-stats=N
                           with --follow=name, reopen a FILE which has not
                           changed size after N (default 5) iterations
                           to see if it has been unlinked or renamed
                           (this is the usual case of rotated log files).
                           With inotify, this option is rarely useful.
      --pid=PID            with -f, terminate after process ID, PID dies--指定进程id,可以结合-f参数一起使用，当指定的进程终止时显示也终止
  -q, --quiet, --silent    never output headers giving file names ###同时显示多个文件时不输出文件名
      --retry              keep trying to open a file even when it is or当连接的文件突然不可访问时尝试重新连接
                             becomes inaccessible; useful when following by
                             name, i.e., with --follow=name
  -s, --sleep-interval=N   with -f, sleep for approximately N seconds当使用-f参数时可以，使用-s显示间隔
                             (default 1.0) between iterations.
                           With inotify and --pid=P, check process P at
                           least once every N seconds.
  -v, --verbose            always output headers giving file names
      --help     display this help and exit
      --version  output version information and exit

If the first character of K (the number of bytes or lines) is a `+‘,
print beginning with the Kth item from the start of each file, otherwise,
print the last K items in the file.  K may have a multiplier suffix:
b 512, kB 1000, K 1024, MB 1000*1000, M 1024*1024,
GB 1000*1000*1000, G 1024*1024*1024, and so on for T, P, E, Z, Y.

tail -f /tmp/orzdba_mysql.log 

tail -f /tmp/orzdba_mysql.log --pid=8770